Process for the direct production of positive photographic images



May 24, 1955 E WEYDE 2 709 13 PROCESS FOR THE DIRECT PRDDUCTION 1 5 CFPOSITIVE PHOTOGRAPHIC IMAGES Filed March 28, 1951 coLLo/0 LAYERCONTAINING HYPO 3 ZIIIIIIIIlI/g WATER PERMEABLE PAPER SILVERHALIDEEMULSION, LAYER CUNTAIN/NG PHOTOGRAPH/0 DEVELDPER PAPH? BASE INVENTOR:

EDITl-I WEYDE 43, ATTORNEYS United States Patent Ofiiee 2,709,135Patented May 24, 1955 PROCESS FOR THE DIRECT PRODUCTION OF POSITIVEPHOTOGRAPHIC LVIAGES Edith Weyde, Leverkusen-Burrig, Germany, assignorto Agfa Aktiengesellschaft fiir Photofabrilration, Leverkusen, Germany,a corporation of Germany Application March 20, 1951, Serial No. 217,910

Claims priority, application Germany March 29, 1950 4 Claims. (Cl.95-88) This invention relates to a process for the direct production ofpositive photographic images.

It is an object of the invention to produce direct positive silverimages on very thin sheets of a water-permeable material.

Further objects will be apparent from the following description.

In French Patent 879,995 there is described a photographic process forthe direct production of positive images according to which a lightsensitive silver halide emulsion (negative) layer after being exposed toan object is developed in the presence of a silver halide solvent, saidsilver halide emulsion layer being in close contact during saiddeveloping process with a light nonsensitive reception (positive) layercontaining nuclei for development. In this process the exposed part ofthe silver halide layer is developed to a negative image and part of theunexposed silver halide is dissolved and transferred to the receptionlayer where it is reduced by the catalytic action of the nuclei fordevelopment to a positive silver image. sists in applying said negativelayer and said reception layer to separate supports and in pressingtogether both layers during the developing process, whereafter these areseparated from each other. In this process it has proved to beadvantageous to incorporate the developing substances in the negativesilver halide layer and the substance required for dissolving thenon-exposed silver halide, for instance, sodium hyposulphite, in thepositive layer. For this purpose, the reception material has to beprovided with a coating, for instance, of gelatine or anotherwater-permeable colloid, containing the silver halide solvent and thenuclei for development required for producing the positive image. Thisprocess is particularly suited for the production of technical prints,for instance, for the reproduction of drawings, documents etc. If thepositive images are produced on transparent reception layers they may beused as intermediate prints for the diazo type process. The receptionmaterial used for this process cannot be produced in any desiredthickness, since the colloids containing the silver halide solvents canbe applied only to relatively thick supports. Therefore, it was notpossible up to the present to obtain prints on very thin materials, forinstance, on paper customarily used for air-mail.

In accordance with the present invention it has been found that directpositive images are produced on extra ordinarily thin, water-permeablematerials, for instance, sheets of regenerated cellulose or sheets ofpaper weighing about 15-30 grams per square meter, by placing suchsheets in the process referred to above between the light sensitivesilver halide layer containing a developing substance and a paper orfilm support of normal thickness coated with a layer containing thesilver halide solvents and, if desired, nuclei for development, andafter soaking with an alkaline solution, pressing together all threelayers, preferable mechanically. The silver halide solvent dissolves inthe developing solution, passes through One embodiment of said processconthe very thin intermediate sheet of paper, regenerated cellulose etc.and dissolves at least part of the nonexposed silver halide of thenegative layer. Thereupon the dissolved silver salts ditiuse backwardsto the thin sheet of paper, regenerated cellulose etc. where the greaterpart thereof is retained and reduced to form a positive silver image.Even in case the layer with the silver halide solvents containadditional nuclei for development the positive image is produced almostexclusively on the thin, intermediate sheet of paper, regeneratedcellulose etc. After separating the three layers after about 1 minute,generally a rather weak positive image is obtained on the thin,intermediate sheet of water-permeable material if the latter does notcontain nuclei for development. A perfect image of the object isobtained by using an intermediate sheet containing nuclei fordevelopment. Nuclei for development are substances which causecatalytically the reduction of the dissolved silver halide by thedeveloping substances after their diitusion into the reception material.By way of example there may be cited colloidal silver, colloidal silversulfide, colloidal silver selenide, colloidal silver telluride,colloidal gold. Furthermore, there may be used substances as, forinstance, sodium sulfide, from which the nuclei for development areformed during the development.

The nuclei for development or the substances producing them may beincorporated in the intermediate sheet in different manner. The sheetsare, for instance, impregnated With solutions containing nuclei fordevelopment, such as colloidal silver. They may also be bathed in dilutesolutions of silver nitrate as, for instance, in an alcoholic solutioncontaining 0.001% silver nitrate.

Furthermore, it is possible to incorporate these nuclei for developmentin the thin sheets already during their production. When employingdifferent types of thin paper, it may happen that the positive imageproduced thereon-also without a previous special treatment for theproduction of nuclei for development-is very different in strength.Apparently some kinds of paper contain substances (originating from thegluing process which may act as nuclei for development so that theaddition of special nuclei for development or substances producing suchnuclei for development may be dispensed with.

The process of the present invention may be varied Within wide limits.Thus, it is possible, for instance, to add at least part of thedeveloping substance and/or the silver halide solvent to the developingsolution. Furthermore, the thin sheet on which the positive images areto be produced and/ or the silver halide emulsion may contain substancesinfluencing the tone of the image, for instance, mercapto compounds.Such substances are described, for instance, in German Patent 473,000.

The invention will be further illustrated by the fol lowing example andin the drawing in which a crosssection of the materials described in theexample is shown in the order in which they are pressed together duringdevelopment.

Example A light sensitive material is obtained by coating photographicpaper 1 of normal thickness (85 g./m. with a silver-chloride-bromideemulsion layer 2 containing per liter 20 g. of hydroquinone, 20 g. ofpotassium metabisulfite and 0.05 g. of 1-phenyll-rnercaptotetrazole(coating thickness corresponding to 1-15 g. of silver/ m.**). For theproduction of the reception layer 4 there is coated an 8% gelatinesolution containing 30 g. of NazSzOs per liter, on a paper support 5. Asa thin, intermediate layer 3 there is used a weakly sized thin typeaswriting paper (Weighing 30 g./m. which is immersed in at 0.01% solutionof colloidal silver and dried. After the exposure of the light sensitivelayer to an object, the latter as well as the intermediate layer and thereception layer .are drawn through a solution containing per liter ofwater 100 g. of sodium sulfite and 20 g. of sodium hydroxide.Immediately after leaving the solution or when still in the solution thethree materials are pressed together in such a Way that one side of theintermediate layer is in contact with the light sensitive layer and theother side with the reception layer. It is also possible to immerse onlyone or two of the materials in the developing solution. After about 1minute the materials are separated from each other. There is obtained apositive image on the thin, intermediate layer.

I claim:

1. A process for the direct production of photographic positive silverimages by using a light sensitive silver halide emulsion layer coated ona paper support, a separate nonlight-sensitive water-permeable colloidlayer containing a silver halide solvent coated on a support and aseparate thin sheet or" a water-permeable material, having a weight of15-30 grams per square meter which comprises exposing said silver halidelayer to an object, developing said exposed silver halide layer byimmersing it in an alkaline solution in the presence of a photographicdeveloping substance and bringing one side of the thin sheet of awater-permeable material in close contact with the exposed silver halidelayer and the other side with the nonlight-sensitive layer containing asilver halide solvent, so that the exposed part of the emulsion layer isdeveloped to a negative image of the object, whereas part of thenon-exposed silver halide layer is dissolved by the silver halidesolvent after the latter has difiused from the nonlight-sensitive layerthrough the thin sheet of water-permeable material to the silver halidelayer, and the dissolved silver halide is transferred to the thin sheetof water-permeable material, where it is developed by the developingsubstance to a positive image of the object, and subsequently separatingsaid light-sensitive layer and said nonlight-sensitive layer from eachother.

2. A process according to claim 1, wherein the light sensitive silverhalide layer contains a photographic developing substance.

3. A process according to claim 2, wherein the light sensitive silverhalide layer contains a mercapto compound.

4. A process according to claim 1, wherein the thin sheet ofwater-permeable material contains nuclei for development.

References Cited in the file of this patent- UNITED STATES PATENTS2,500,421 Land Mar. '12, 1950 2,543,181 Land Feb. 27, 1951 2,584,030Land Jan. 29, 1952 2,635,048 Land Apr. 14, 1953 2,647,056 Land July 28,1953 OTHER REFERENCES Varden: PSA Journal, vol. 13, September 1947, .pp.551-554.

Land: The Photographic Journal, vol. 90A, pp. 7-15, January 1950.

1. A PROCESS FOR THE DIRECT PRODUCTION OF PHOTOGRAPHIC POSITIVE SILVER IMAGE BY USING A LIGHT SENSITIVE SILVER HALIDE EMULSION LAYER COATED ON A PAPER SUPPORT, A SEPARATE NONLIGHT-SENSITIVE WATER-PERMEABLE COLLOID LAYER CONTAINING A SILVER HALIDE SOLVENT COATED ON A SUPPORT AND A SEPARATE THIN SHEET OF A WATER-PERMEABLE MATERIAL HAVING A WEIGHT OF 15-30 GRAMS PER SQUARE METER WHICH COMPRISES EXPOSING SAID SILVER HALIDE LAYER TO AN OBJECT, DEVELOPING SAID EXPOSED SILVER HALIDE LAYER BY IMMERSING IT IN AN ALKALINE SOLUTION IN THE PRESSURE OF A PHOTOGRAPHIC DEVELOPING SUBSTANCE AND BRINGING ONE SIDE OF THE THIN SHEET OF A WATER-PERMEABLE MATERIAL IN CLOSE CONTACT WITH THE EXPOSED SILVER HALIDE LAYER AND THE OTHER SIDE WITH THE NONLIGHT-SENSITIVE LAYER CONTAINING A SILVER HALIDE SOLVENT, SO THAT THE EXPOSED PART OF THE EMULSION LAYER IS DEVELOPED TO A NEGATIVE IMAGE OF THE OBJECT WHEREAS PART OF THE NON-EXPOSED SILVER AFTER THE LATTER DISSOLVED BY THE SILVER HALIDE SOLVENT HALIDE LAYER IS HAS DIFFUSED FROM THE NONLIGHT-SENSITIVE LAYER THROUGH THE THIN SHEET OF WATER-PERMEABLE MATERIAL TO THE SILVER HALIDE LAYER, AND THE DISSOLVED SILVER HALTE IS TRANSFERRED TO THE THIN SHEET OF WATER-PERMEABLE MATERIAL WHERE IT IS DEVELOPED BY THE DEVELOPING SUBSTANCE TO A POSITIVE IMAGE OF THE OBJECT, AND SUBSEQUENTLY SEPARATING SAID LIGHT-SENSITIVE LAYER AND SAID NONLIGHT-SENSITIVE LAYER FROM EACH OTHER. 